1. Field of the Invention
The present invention relates generally to a toothed belt having functions of aiding in positioning and mounting a desired attachment or part on a predetermined position thereof and identifying that predetermined position, which will hereinafter also be called a "positioning-aiding and position-identifying toothed belt"). More particularly, the present invention relates to a positioning-aiding and position-identifying toothed belt which can be suitably used as a carriage belt for a printer.
2. Description of the Related Art
Toothed belts generally comprise a laminated structure of a tooth rubber member, a backing rubber member and a core wire or tension member embedded between the tooth rubber member and the backing rubber member. To manufacture such toothed belts, an unvulcanized rubber compound sheet, which will be ultimately formed into the above-mentioned tooth rubber and backing rubber members, is wound around a cylindrical tooth-forming die having a tooth cloth sheet and a tension member previously wrapped therearound, so that the rubber compound sheet is formed into a predetermined shape and vulcanized. The resultant vulcanized rubber compound sheet is then cut into rings of predetermined widths to provide a plurality of endless toothed belts.
In recent years, such a toothed belt has been used popularly as a carriage belt of a printer, as schematically illustrated in FIG. 4. In this illustrated example, the printer carriage belt has a toothed belt portion with a series of driven teeth 10 formed in the inner surface of the belt along part of its length, and a flat belt portion with a non-toothed or flat inner surface. The toothed belt portion with the driven teeth 10 is wound around and engaged with a pulley P1 with driving teeth (hereinafter "driving toothed pulley"), while the flat belt portion is wound around a non-toothed follower pulley P2. Printer carriage C is mounted on a boundary region between the toothed belt portion and the flat belt portion, so that the printer carriage C performs a printing function by being reciprocally moved over a predetermined distance as the toothed carriage belt is driven via the driving toothed pulley P1.
In the past, the printer carriage C was mounted on the toothed carriage belt by mounting pieces, projecting from the body of the carriage C, being pressed against the inner and outer surfaces of the carriage belt to thereby tightly grip the belt across the belt's thickness, using a visual carriage-positioning mark put at a predetermined position on the outer surface of the carriage belt.
Although the toothed carriage belt with the visual carriage positioning mark allowed a human operator to attach the printer carriage C accurately to the predetermined position while being guided by the positioning mark, manufacturing such a toothed carriage belt required an additional step of putting the positioning mark on the belt, which considerably increased the costs of the carriage belt. In addition, the printer carriage was apt to be undesirably displaced in position during the mounting operation, which resulted in poor reliability of the mounting operation.
With a view to providing solutions to the above-discussed problems, an improved toothed belt has been proposed, which, as shown in FIG. 5, includes a positioning-aiding/position-identifying tooth 12 formed integrally on the tooth rubber member and having a length substantially equal to a sum of the lengths of two driven teeth 10 and one groove between the two driven teeth 10. With the proposed toothed belt, the human operator can readily ascertain the carriage-mounting position by both the outer appearance and the actual touch of the positioning-aiding/position-identifying tooth 12 which are different from those of the driven teeth 10, and thereby effectively prevent the positional displacement and deviation of the printer carriage from occurring during the mounting operation.
However, the proposed toothed belt is not satisfactory for the following reasons. Forming the positioning-aiding/position-identifying tooth 12, having the length substantially equal to two driven teeth 10 and one intervening groove as shown in FIG. 5, unavoidably results in a shortage of the tooth rubber material between two driven teeth 10 adjacent to the positioning-aiding/position-identifying tooth 12. This tooth rubber shortage leads to insufficient projection or height of the positioning-aiding/position-identifying tooth 12, which would prevent accurate mounting of the printer carriage C on the predetermined position of the belt. If some attempt is made to form the positioning-aiding/position-identifying tooth 12 into a sufficient height or projection, then there would be caused a shortage of the backing rubber material behind the positioning-aiding/position-identifying tooth 12, which would produce a recess in the outer surface of the tooth belt. In such a case, the tension member 30, which should have been embedded completely between the tooth rubber member and the backing rubber member, tends to be exposed and the rubber is apt to scale off the belt body, which would reduce the durability of the toothed belt. Consequently, there arises the problem that a desired part, such as a printer carriage, can not be properly mounted on a predetermined position of the proposed toothed belt.
As one approach to eliminate the problems encountered by the proposed toothed belt, an attempt has been made to feed a sufficient amount of the rubber material to the portion of the toothed belt where the positioning-aiding/position-identifying tooth 12 is to be formed. However, this approach is also disadvantageous in that there arises a need not only to change a belt-forming die provided with the cylindrical tooth forming die but also to set special conditions for feeding the unvulcanized rubber compound sheet and special conditions for shaping, vulcanizing, etc. of the unvulcanized rubber compound sheet, so that the belt manufacturing process would become very complex and the manufacturing costs of the toothed belt would increase accordingly.
Similar problems would arise even where the tooth belt is used as a belt for taking out information from a predetermined position of the belt; that is, it is not possible to accurately recognize information, indicative of a printing position or the like, that should be transmitted from the predetermined position.